Sewage samples reveal how little we know about viruses

Viruses -- nasty infectious agents that replicate inside the
living cells of organisms -- are by far the most abundant life form
on the planet. But our knowledge of the viral kingdom is just a tiny fraction of the total number of
unique viruses that inhabit all two-million-odd species on
Earth.

Take, for instance, the pipes running underneath your feet.
Researchers from universities in Pittsburgh, St. Louis and
Barcelona grabbed samples of raw sewage from pipes in North
America, Europe and Africa to investigate the diversity of viruses present in our waste.

Virologists have about 3,027 viruses on record. In those sewage
samples the research team found 234
known viruses, and a whopping 43,381 unique sequences that have
never been formally identified before.

Of those known viruses, 17 were ones that target humans like
Human papillomavirus and norovirus, which causes diarrhea. There
are plenty of viruses belonging to sewer occupants like rats and
cockroaches, and plenty of bacteriophages,
which are viruses that only attack bacteria.

A huge number of the known viruses were associated with plants,
down to use humans and our veggie eating habits -- plant viruses
outnumber all other types of viruses in human stool, after all. One
for the fact fans, there.

Those vast majority of unknown viruses are generally left
undiscovered as they do not target humans or our pets or our live
stock. But we ignore these threats at our peril because emerging
viruses and ones that leap from species to species can soon target
humans, as we've seen in HIV, Ebola, H5N1 bird flu and many
more.

So the multi-national team of researchers want to better
catalogue the virus universe, to get a better understanding of
these emerging threats.

"First you have to see the forest before you can pick out a
particular tree to work on," said the University of Pittsburgh
professor James Pipas. "If gene
exchange is occurring among viruses, then we want to know where
those genes are coming from, and if we only know about a small
percentage of the viruses that exist, then we're missing most of
the forest."